Core analysis is widely practised throughout the oil and gas exploration industry in order to determine various properties of the drilling formation. Analysis of the core generally involves removing the core from the formation and transporting it to the surface where it can subsequently be analysed. In order to obtain accurate and useful information from the analysis, it is important that the properties of the core at the surface are an accurate representation of the core properties downhole. In order to maintain core property measurements representative of the downhole conditions, it is important that, during removal to the surface, the surrounding pressure of the core sample is maintained at a pressure which is high enough to prevent any fluid present in the sample from escaping and thereby damaging the sample. Accordingly, it would be desirable to be able to retain the fluids within the sample.
Current methods of extracting the sample from the downhole environment at relatively high pressure involve passing the core sample into an inner barrel (whilst downhole) which has a pressure valve at each end. Once the core sample has entered the inner barrel, the pressure valves are actuated in order to seal in the core sample at the surrounding downhole pressure. The inner barrel is then retrieved to the surface of the well and the highly pressurised (relative to the outside surface ambient pressure or atmospheric pressure) inner barrel is removed for analysis. This method has the disadvantage of being dangerous to persons operating the well since there exists the possibility of the high pressure, thin walled inner barrel exploding, thereby causing serious injury.